JP3465675B2 - Piezoelectric / electrostrictive film type element - Google Patents

Abstract

A ceramic substrate 1 comprises a thin diaphragm portion 3 and a thick portion 2. A lower electrode 4 is formed on the ceramic substrate and is spaced apart from an auxiliary electrode 8, also formed on the ceramic substrate. A bonding layer 7C comprises an insulator and is formed on the ceramic substrate between the lower and auxiliary electrodes. A piezoelectric/electrostrictive layer 5 is formed on at least a portion of each of the lower electrode, the auxiliary electrode and the bonding layer. An upper electrode 6 extends over the piezoelectric/electrostrictive layer and contacts the auxiliary electrode. A bonded portion exist wherein the bonding layer serves to completely bond together the substrate and the piezoelectric/electrostrictive film layer. <IMAGE>

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric / electrostrictive film type element, and in particular, an actuator utilizing bending displacement, a sensor for fluid characteristics, sound pressure, minute weight, acceleration, etc., such as a microphone or a viscosity sensor. The present invention relates to a piezoelectric / electrostrictive film type element used in.

[0002]

2. Description of the Related Art Piezoelectric / electrostrictive electrostrictive film type elements have been conventionally used as actuators and various sensors. The piezoelectric / electrostrictive film type element used as a sensor is used for measuring characteristics such as density, concentration and viscosity of a fluid as disclosed in, for example, Japanese Patent Laid-Open No. 8-201265. Such an element is used as a sensor by utilizing the fact that there is a correlation between the amplitude of the piezoelectric vibrator and the viscous resistance of the fluid in contact with the vibrator. A vibration form in a mechanical system such as a vibration of a vibrator can be replaced with an equivalent circuit in an electric system, which vibrates a piezoelectric / electrostrictive film type vibrator in a fluid, and this vibrator viscous resistance of the fluid. It is possible to detect changes in the electrical constants of the equivalent circuit of the piezoelectric body that constitutes the vibrator by receiving mechanical resistance based on the above, and measure the characteristics such as viscosity, density, and concentration of the fluid. . The measurable fluid means a liquid and a gas, and not only a liquid composed of a single component such as water, alcohol, or oil, but a medium soluble or insoluble in these liquids is dissolved, mixed or suspended. Includes liquids, slurries and pastes. The electrical constants to be detected include loss coefficient, phase, resistance, reactance, conductance, susceptance, inductance and capacitance. In particular, there is one maximum or minimum change point near the resonance frequency of the equivalent circuit. A loss factor or phase is preferably used. With this, not only the viscosity of the fluid but also the density and the concentration can be measured, and for example, the sulfuric acid concentration in the sulfuric acid aqueous solution can be measured. It should be noted that, as an index for detecting a change in vibration form, a change in resonance frequency can be used as well as an electric constant, as long as there is no particular problem from the viewpoint of measurement accuracy and durability.

Such a piezoelectric / electrostrictive film type element is disclosed in FIG. 2 as disclosed in Japanese Patent Laid-Open No. 5-267742.
A thin diaphragm part 3 having a thick part 2 on the periphery as shown in
An auxiliary electrode 8 is formed at a position independent of the lower electrode 4 laminated on the substrate 1 made of ceramics having the above-mentioned structure, and a part of the auxiliary electrode is inserted into a part of the lower side of the piezoelectric / electrostrictive film 5. Is formed. With such a configuration, the upper electrode 6 can be continuously formed on the surfaces of the auxiliary electrode 8 and the piezoelectric / electrostrictive film 5 without disconnection, and the reliability of connection of the upper electrode 6 is improved. In FIG. 2, the fluid to be measured exists in the cavity 10 and the through hole 9
Introduced by.

Further, in such a piezoelectric / electrostrictive film type element, as disclosed in JP-A-6-260694, the piezoelectric / electrostrictive film 5 on the lower electrode 4 is provided as shown in FIG. ,
The size may cover the lower electrode 4 and the peripheral portion of the piezoelectric / electrostrictive film 5 may project to the ceramic substrate 1. This eliminates the need for precise alignment of the lower electrode 4 and the piezoelectric / electrostrictive film 5 and easily prevents a short circuit between the upper and lower electrodes. Further, the protruding portion 11 of the piezoelectric / electrostrictive film 5 is incompletely bonded to the substrate 1 to form the incompletely bonded portion 7A, so that the protruding portion 11 is not bonded to the substrate. It is possible to develop sufficient bending displacement, generated force, and vibration. The incompletely bonded state means a state in which a part of the overhanging portion is partially bonded to the ceramic substrate or an unbonded state in which there is no bonded portion at all. Peel (peeling off)
The strength is 0.5 kg / mm ² or less. The formation of such an incompletely bonded state is performed by selecting the substrate material and the piezoelectric / electrostrictive material so that the mutual reactivity is low, and the piezoelectric / electrostrictive film and the substrate are directly contacted with each other. In some cases, the piezoelectric / electrostrictive film 5 may be formed after forming the dummy layer so as not to do so. A stamping method, a screen printing method, or an inkjet method is suitably used for forming the dummy layer. When the piezoelectric / electrostrictive film 5 is heat-treated for sintering, the dummy layer is formed of a material that burns and disappears by this heat treatment, for example, a resin material, and the incompletely bonded portion 7A is formed after the disappearance. It is. Alternatively, when the piezoelectric / electrostrictive film and the upper electrode are not heat-treated, the dummy layer is formed of a resin material that dissolves in water or an organic solvent, and after the piezoelectric / electrostrictive film 5 is formed or the piezoelectric / electrostrictive film 5 is formed. After the upper electrode 6 is formed, it is dissolved and removed by water, an organic solvent or the like to form the incompletely bonded portion 7A.

[0005]

In a sensor element that performs sensing by detecting the electrical characteristics of such vibrations, it is desirable that the electrical characteristics do not vary, whereas the conventional piezoelectric elements. / In the structure of the electrostrictive film type element, the initial electric constant may vary among the element solids, or the electric constant may change over time.
In such a case, it was necessary to take the trouble of fine adjustment.

[0006]

Therefore, as a result of research, in the conventional piezoelectric / electrostrictive film type element, as shown in FIG. 2, an incompletely bonded state similar to the incompletely bonded portion 7A of the overhanging portion 11 is obtained. The incompletely coupled portion 7B is formed between the lower electrode 4 and the auxiliary electrode 8 over the thin diaphragm 3 and the thick portion 2 of the substrate, and is not applicable to a sensor element or the like utilizing an electric constant in vibration. It has been found that such a variation in the incompletely bonded state of the incompletely bonded portion 7B and a change with time are one of the main causes of the change in the vibration form and the change in the electric constant. In other words, since the incompletely bonded state cannot be stably formed with good reproducibility, the thin diaphragm part vibrates or displaces during actual use, so that the partial connection may be lost. , Phenomenon such as generation of microcracks occurs.

The present invention is a piezoelectric / electrostrictive device in which a lower electrode and an auxiliary electrode, a piezoelectric / electrostrictive film, and an upper electrode are sequentially laminated on a substrate made of ceramics having a thin diaphragm portion having a thick portion on its peripheral portion. A piezoelectric / electrostrictive device, which is a strained film type element, in which a piezoelectric / electrostrictive film and a ceramic substrate are completely bonded by providing a bonding layer made of an insulator between a lower electrode and an auxiliary electrode. It is a film type device. Completely bonded state means peeling of the piezoelectric / electrostrictive film after the substrate, bonding layer, and piezoelectric / electrostrictive film have been integrated.
It means a state where the strength is 2 kg / mm ² or more.

As the piezoelectric / electrostrictive film, lead titanate,
It is preferably composed of a material containing at least one selected from lead zirconate, lead magnesium niobate, and lead nickel niobate as a main component.

Further, the piezoelectric / electrostrictive film is (Bi _0.5 Na _0.5 ).
It is preferably composed TiO ₃ or containing a material whose main component, and further, the piezoelectric / electrostrictive film is (1-x)
_{(Bi 0 .5 Na 0.5) TiO} 3 -xKNbO 3 (x is 0 ≦ x ≦ mole fraction
0.06) or a material containing this as a main component is more preferable.

It is more preferable that the bonding layer made of the above-mentioned insulator is glass having a softening point equal to or higher than the heat treatment temperature of the piezoelectric / electrostrictive film.

In addition, the piezoelectric / electrostrictive film is (Bi _0.5 Na _0.5 ) Ti
O ₃ or a material containing it as a main component, or (1-x)
(Bi _0.5 Na _0.5 ) TiO ₃ −xKNbO ₃ (x is a mole fraction, 0 ≦ x ≦
0.06) or a material containing this as a main component, (1-x) (Bi _0.5 Na
_0.5 ) TiO ₃ −xKNbO ₃ (x is a mole fraction 0.08 ≦ x ≦ 0.5) By providing a bonding layer composed of a material having a main component, the piezoelectric / electrostrictive film and the ceramic substrate are completely bonded. can do.

[0012]

1 shows an embodiment of a piezoelectric / electrostrictive film type element of the present invention. Such a piezoelectric / electrostrictive film type element has a lower electrode 4 and an auxiliary electrode 8 on a ceramic substrate 1 composed of a thin diaphragm portion 3 and a thick portion 2.
Then, the piezoelectric / electrostrictive film 5 and the upper electrode 6 are formed as an integral structure by sequentially laminating by a normal film forming method. Between the lower electrode 4 and the auxiliary electrode 8, the piezoelectric / electrostrictive film and the ceramic substrate are in a completely bonded state by the bonding layer 7C made of an insulator. In the present invention, the overhanging portion 11 is not always necessary,
The lower electrode 4 and the piezoelectric / electrostrictive film 5 may have substantially the same size when it is required to further reduce variations in the electric constants as element characteristics and changes over time.

The material of the ceramic substrate 1 is preferably a material having heat resistance, chemical stability and insulation. This is because heat treatment may be performed when the lower electrode 4, the piezoelectric / electrostrictive film 5 and the upper electrode 6 are integrated as described later, and the piezoelectric / electrostrictive film type element as a sensor element has a liquid characteristic. This is because the liquid may have conductivity or corrosiveness when sensing. Examples of ceramics that can be used from this point of view include stabilized zirconium oxide, aluminum oxide, magnesium oxide, mullite, aluminum nitride, silicon nitride and glass. Among these, stabilized zirconium oxide can be preferably used because it can maintain high mechanical strength and excellent toughness even when the thin diaphragm portion is formed thinly.

Thin diaphragm portion 2 of ceramic substrate 1
The thickness of is generally 50 μm or less, preferably 30 μm or less, and more preferably 15 μm or less in order not to disturb the vibration of the piezoelectric / electrostrictive film. The surface shape of the thin diaphragm portion can be any shape such as rectangle, square, triangle, ellipse, and true circle, but in the application of the sensor element that needs to simplify the excited resonance mode, the shape of the rectangle or true The circular shape is selected as needed.

On the surface of such a ceramic substrate 1,
The lower electrode 4 and the auxiliary electrode 8 are formed. The lower electrode 4 is formed from one end of the ceramic substrate to a predetermined size equal to or smaller than the size on the thin diaphragm portion 3 where the piezoelectric / electrostrictive film 5 is to be formed.
One end of the lower electrode 4 is used as a lead terminal. On the other hand, the auxiliary electrode 8 is formed from the end of the ceramic substrate 1 opposite to the lower electrode 4 toward the thin diaphragm 3 to a predetermined position. One end of the auxiliary electrode 8 is used as a lead terminal.

The lower electrode 4 and the auxiliary electrode 8 may be made of different materials or the same material.
A conductive material having good bonding properties with the electrostrictive film 5 is used. Specifically, platinum, palladium, rhodium,
An electrode material containing silver or an alloy thereof as a main component is preferably used. Particularly, when heat treatment for sintering is performed when forming the piezoelectric / electrostrictive film, platinum and dust are removed. An alloy containing the main component is preferably used.

For forming the lower electrode 4 and the auxiliary electrode 8, various known film forming methods are used. Specifically, thin film forming methods such as ion beam, sputtering, vacuum deposition, CVD, ion plating, and plating, and thick film forming methods such as screen printing, spraying, and dipping are appropriately selected. Method and screen printing method are suitably selected.

Prior to the formation of the piezoelectric / electrostrictive film 5, the piezoelectric / electrostrictive film 5 and the ceramic substrate 1, the lower electrode 4 and the auxiliary electrode 8 are formed.
In the meantime, a bonding layer 7C made of an insulating material for forming a completely bonded state is formed. As the bonding layer 7C made of an insulating material, any material such as an organic material or an inorganic material may be used as long as it has high adhesiveness and bondability with both the piezoelectric / electrostrictive film 5 and the ceramic substrate 1. Further, the coefficient of thermal expansion of the material used for the bonding layer 7C has an intermediate value between the coefficient of thermal expansion of the material of the substrate and the coefficient of thermal expansion of the material used for the piezoelectric / electrostrictive film 5, and the highly reliable bondability is obtained. Is more preferable because
When the piezoelectric / electrostrictive film 5 is heat treated for sintering,
As a material forming the coupling layer 7C, a glass material is piezoelectric /
A glass material having a softening point equal to or higher than the heat treatment temperature of the piezoelectric / electrostrictive film 5 is preferably used because it has high adhesion and bondability with both the electrostrictive film 5 and the ceramic substrate 1. 5 and the substrate 1 are more firmly bonded, and since the softening point is high, deformation due to heat treatment can be suppressed,
It is more preferably used.

Further, the piezoelectric / electrostrictive film 5 is formed by (Bi _0.5
Na _0.5 ) TiO ₃ or a material containing it as a main component, or (1
-X) (Bi _0.5 Na _0.5 ) TiO ₃ -x KNbO ₃ (x is a mole fraction of 0
When ≦ x ≦ 0.06) or composed of a material mainly containing this, (1-x) (Bi 0. 5 Na 0.5) TiO 3 -xKNbO
_The bonding layer 7C made of a material containing ₃ (x is a mole fraction of 0.08 ≦ x ≦ 0.5) as a main component has high adhesiveness with both the piezoelectric / electrostrictive film 5 and the ceramic substrate 1, Piezoelectricity /
Since adverse effects on the electrostrictive film 5 and the substrate 1 can be suppressed,
It is more preferably used. That is, the coupling layer 7C is (1-
x) (Bi _0.5 Na _0.5 ) TiO ₃ −xKNbO ₃ (x is 0.08 in mole fraction)
≦ x ≦ 0.5), since it has the same components as the piezoelectric / electrostrictive film 5, the adhesiveness with the piezoelectric / electrostrictive film 5 is high,
Further, there is little problem due to diffusion of a different element that tends to occur when glass is used, and since a large amount of KNbO ₃ is contained, it has high reactivity with the substrate and a strong bond is possible. In addition, (1-
_{x) (Bi 0 .5 Na 0.5} ) TiO 3 -xKNbO 3 (x is the mole fraction 0.08
Since ≦ x ≦ 0.5) shows almost no piezoelectric characteristics, vibration, displacement and stress do not occur with respect to the electric field generated in the lower electrode 4 and the auxiliary electrode 8 during use, so stable element characteristics can be obtained.

A usual thick film method is used for forming these bonding layers 7C, and particularly, the stamping method, the screen printing method, or the size of the portion to be formed is several tens of μm to several tens.
In the case of about 100 μm, the inkjet method is preferably used. When heat treatment of the bonding layer 7C is required,
It may be heat-treated before forming the next piezoelectric / electrostrictive film 5,
Heat treatment may be performed simultaneously after the formation of the piezoelectric / electrostrictive film 5.

The piezoelectric / electrostrictive film 5 extends over the lower electrode 4, the auxiliary electrode 8 and the coupling layer 7C, and the lower electrode 4
It is formed in a size to cover. The material of the piezoelectric / electrostrictive film may be any material as long as it exhibits a piezoelectric / electrostrictive effect. Examples of such materials include lead zirconate, lead titanate, and lead zirconate titanate (PZT). Lead-based ceramic piezoelectric / electrostrictive materials, barium titanate and titanium-based ceramic ferroelectrics containing them as a main component, polymer piezoelectric materials typified by polyvinylidene fluoride (PVDF), or (Bi _0.5 Na _0.5 ) Bi-based ceramic piezoelectric materials typified by TiO ₃ and Bi layered ceramics can be mentioned. Of course, it goes without saying that a mixture thereof, a solid solution, or a material obtained by adding an additive thereto, which has improved piezoelectric / electrostrictive properties, can be used. The PZT-based piezoelectric body has high piezoelectric characteristics and is suitably used as a material for a sensor capable of highly sensitive detection. In the present invention, in particular, the substrate is composed of a material containing at least one selected from lead titanate, lead zirconate, lead magnesium niobate, and lead nickel niobate as a main component. It is more preferably used because it has low reactivity with materials, segregation of components during heat treatment does not easily occur, treatment for maintaining the composition can be favorably performed, and a target composition and crystal structure are easily obtained. .

When platinum or an alloy containing platinum as a main component is used for the lower electrode 4 and the auxiliary electrode 8, the bondability with them is higher, the characteristic variation of the element is reduced, and the high reliability is obtained. Since it is obtained, (Bi _0.5 Na _0.5 ).
TiO ₃ or a material containing this as a main component is preferably used. Among these, particularly (1-x) (Bi _0.5 Na _0.5 ) Ti
O ₃ −xKNbO ₃ (x is a mole fraction of 0 ≦ x ≦ 0.06) or a material containing this as a main component is more preferably used because it has relatively high piezoelectric characteristics.

Such a piezoelectric / electrostrictive material is formed as the piezoelectric / electrostrictive film 5 by various known film forming methods like the lower electrode 4 and the auxiliary electrode 8. Among them, screen printing is preferably used from the viewpoint of low cost.

The piezoelectric / electrostrictive film 5 thus formed is indispensable.
If necessary, heat treatment is applied to lower electrode 4, auxiliary electrode 8 and connection.
It is integrated with the composite layer 7C. In the present invention,
In order to suppress characteristic variations and increase reliability, piezoelectric /
The contact between the electrostrictive film 4, the lower electrode 5, the auxiliary electrode 8 and the coupling layer 7C
Since it is necessary to strengthen compatibility, (Bi_0.5Na_0.5) TiO₃
Or the material which has this as a main component, especially (1-x) (Bi
_0.5Na_0.5) TiO₃-XKNbO ₃(X is a mole fraction, 0 ≦ x ≦ 0.0
6) Or using a material containing this as a main component, 900 to 140
Heat treated at a temperature of 0 ° C, preferably 1000 ° C to 1300 ° C
It is preferable. The same applies when using PZT-based materials.
It At this time, the piezoelectric / electrostrictive film 5 should not become unstable at high temperature.
Control the atmosphere together with the evaporation source of the piezoelectric / electrostrictive material.
It is preferable to perform the heat treatment while performing.

Further, the piezoelectric / piezoelectric element thus formed
The upper electrode 6 is continuously formed on the electrostrictive film 5 from the piezoelectric / electrostrictive film 5 to the auxiliary electrode 8. As a material of the upper electrode 6, a conductive material having a high bonding property with the piezoelectric / electrostrictive film 5 is used, and the lower electrode 4 and the auxiliary electrode 8 are used.
It is formed by a film forming method similar to the above. Further, the upper electrode 6 is heat-treated as necessary after the film formation and is joined to the piezoelectric / electrostrictive film 5 and the auxiliary electrode 8 to form an integrated structure. Similar to the lower electrode 4, such heat treatment is not always necessary.

When the lower electrode 4, the bonding layer, the piezoelectric / electrostrictive film 5, and the upper electrode 6 are bonded by heat treatment, they may be heat-treated each time they are formed, or they may be sequentially formed after film formation. At the same time, heat treatment may be performed. When heat treatment
It goes without saying that the heat treatment temperature is appropriately selected in order to obtain good bondability and suppress alteration due to diffusion of constituent elements. Although the through hole 9 is formed in the cavity 10 in FIG. 1, the structure of the cavity 10 and below in which the element contacts the fluid is
Any structure such as a simple cavity structure without a lid may be used without limitation.

[0027]

In the piezoelectric / electrostrictive film type element according to the present invention, since the piezoelectric / electrostrictive film and the substrate are completely coupled between the lower electrode and the auxiliary electrode, there are variations in vibration and changes with time. Therefore, a suitable element can be obtained as an element for discriminating fluid characteristics or liquid / gas by detecting an electric constant in vibration, a measuring element for sound pressure, minute weight, acceleration, etc., and an actuator element. .

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a piezoelectric / electrostrictive film type element for sensor of the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of a conventional piezoelectric / electrostrictive film type element for a sensor.

[Explanation of symbols]

1 ... Board, 2 ... Thick part, 3 ... Diaphragm part, 4
..Lower electrode, 5 ... Piezoelectric / electrostrictive film, 6 ... Upper electrode,
7A, 7B ... Incompletely joined part, 7C ... Joined layer, 8 ...
Auxiliary electrode, 9 ... through hole, 10 ... cavity.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 41/09

Claims (6)

(57) [Claims] 1. A piezoelectric / electrostrictive film in which a lower electrode and an auxiliary electrode, a piezoelectric / electrostrictive film, and an upper electrode are sequentially laminated on a substrate made of ceramics having a thin diaphragm part having a thick part on a peripheral portion. Piezoelectric / electrostrictive film type, characterized in that the piezoelectric / electrostrictive film and the ceramic substrate are completely bonded by providing a bonding layer made of an insulator between the lower electrode and the auxiliary electrode. element. 2. The piezoelectric / electrostrictive film is made of a material containing at least one selected from lead titanate, lead zirconate, lead magnesium niobate, and lead nickel niobate as a main component. 1. The piezoelectric / electrostrictive film type device according to 1. 3. The piezoelectric / electrostrictive film is (Bi _0.5 Na _0.5 ) TiO ₃
Alternatively, the piezoelectric / electrostrictive film type element according to claim 1, which is made of a material containing this as a main component. 4. The piezoelectric / electrostrictive film is (1-x) (Bi_0.5
Na_0.5) TiO₃-XKNbO ₃(X is a mole fraction 0 ≦ x ≦ 0.06)
Or composed of a material containing this as a main component.
Piezoelectric / electrostrictive film type device. 5. The piezoelectric / coupling layer comprising the insulating layer
The piezoelectric / electrostrictive film type element according to any one of claims 1 to 4, which is a glass having a softening point equal to or higher than a heat treatment temperature of the electrostrictive film. 6. The bonding layer formed of the insulator is (1-
x) (Bi _0.5 Na _0.5 ) TiO ₃ −xKNbO ₃ (x is 0.08 in mole fraction)
The piezoelectric / electrostrictive film type element according to claim 3 or 4, wherein the piezoelectric / electrostrictive film type element is made of a material containing ≤x≤0.5) as a main component.